update react router to v8

interface/src/preact-react-shim.ts

@@ -0,0 +1,62 @@
+// preact/compat shim used as the `react` alias.
+//
+// react-router v8 statically imports/uses a couple of React 19 APIs that
+// preact/compat doesn't implement. Aliasing `react` straight to preact/compat
+// therefore (a) fails Rolldown's static export analysis during dependency
+// optimization / build and (b) could crash at runtime. We re-export everything
+// from preact/compat and add the missing pieces:
+//
+//   - useOptimistic: called unconditionally at the top of `RouterProvider`
+//     (lib/components.js). The optimistic setter is only invoked when
+//     `unstable_useTransitions === true`, which this app doesn't enable, so a
+//     passthrough state + no-op setter is correct.
+//   - use: only invoked (on a promise) in react-router's RSC server-SSR path
+//     (lib/rsc/server.ssr.js), which a client-only `createBrowserRouter` app
+//     never executes. It still must exist as an export to avoid Rolldown's
+//     IMPORT_IS_UNDEFINED warning; we provide a Suspense-style promise unwrap
+//     just in case it is ever reached.
+
+// preact/compat's type declarations use CommonJS `export =`, which TypeScript
+// won't let us `export *` from, but Rolldown/Vite correctly re-export its named
+// members at runtime (this is what makes react-router's `React.useState` etc.
+// resolve through the alias).
+// @ts-expect-error -- CJS `export =` interop; valid at bundle time.
+export * from 'preact/compat';
+export { default } from 'preact/compat';
+
+export function useOptimistic<S>(passthrough: S): [S, (action: unknown) => void] {
+  return [passthrough, () => {}];
+}
+
+interface TrackedThenable<T> extends PromiseLike<T> {
+  status?: 'pending' | 'fulfilled' | 'rejected';
+  value?: T;
+  reason?: unknown;
+}
+
+// React 19's `use`, narrowed to the promise-unwrap (Suspense) behavior that
+// react-router relies on.
+export function use<T>(usable: TrackedThenable<T>): T {
+  switch (usable.status) {
+    case 'fulfilled':
+      return usable.value as T;
+    case 'rejected':
+      throw usable.reason;
+    default:
+      if (usable.status === undefined) {
+        usable.status = 'pending';
+        void usable.then(
+          (value) => {
+            usable.status = 'fulfilled';
+            usable.value = value;
+          },
+          (reason) => {
+            usable.status = 'rejected';
+            usable.reason = reason;
+          }
+        );
+      }
+      // eslint-disable-next-line @typescript-eslint/only-throw-error -- Suspense throws the thenable
+      throw usable;
+  }
+}